The invention relates generally to clutch plates having a specific surface finish and more specifically to clutch plates adapted for use in multiple plate friction clutch packs wherein a mill finish is polished to produce a surface having irregular flat regions and irregular recessed regions.
Amongst motor vehicle manufacturers, two areas of vehicle dynamics are foci of constant study, engineering effort and product improvement. These two areas can broadly be denominated vehicle performance and occupant comfort. Occupant comfort within the context of vehicle dynamics generally addresses noise, vibration and harshness (NVH) issues. These design criteria are nowhere more subjects of concern than in vehicles with adaptive four-wheel drive systems where the complex power train, torque distribution device, control strategy and overall system operation create unique performance and control issues. Such adaptive vehicle drive systems operate under most conditions as two-wheel drive systems and automatically shift or adjust to four-wheel drive when certain operating conditions such as wheel slip or other anomalies are present.
In such systems, the commencement of four-wheel drive operation, typically achieved by engagement of a clutch disposed between the full-time or primary drive line and the part-time or secondary drive line, which transfers drive energy to the secondary drive line, must be carefully controlled so that its operation is unnoticeable to the vehicle driver. Competing with this design criteria for smooth, transparent clutch engagement is often the design preference to engage the clutch as quickly as possible in order to optimize vehicle control and slip regulation. Whether the clutch engages slowly or rapidly, such engagement must be smooth, linear and without grabbing, judder or other engagement phenomena which may be detected by the vehicle driver and passengers. The present invention is directed to a multiple plate friction clutch having improved engagement smoothness and torque through put for use in motor vehicle drive lines.
Friction clutch plates have a first face exhibiting a surface finish of about Ra 0.5 to 0.9 and a second face having friction material secured thereto. The clutch plates are manufactured by rolling steel to a thickness of about 0.030 inches (0.76 mm) which exhibits a mill finish of about Ra 0.64 to 1.14. The rolled steel is then stamped to form circular clutch plate blanks. One surface is then smoothed, preferably by polishing, so that peaks and sharp points are flattened or removed. The resulting surface finish includes irregular relatively flat and smooth regions interspersed with and separating irregular recesses or pits and exhibits a surface finish of about Ra 0.5 to 0.9. Friction material is then secured to the opposite face of the clutch plates. The clutch plates are used in multiple plate friction clutch packs which are intended for use in dual clutch front and rear axle assemblies and motor vehicle transfer cases.
Thus it is an object of the present invention to provide clutch plates or discs having a first friction material surface and a second clutch surface with roughness between Ra 0.5 and 0.9.
It is a further object of the present invention to provide a multiple plate clutch pack assembly having improved engagement characteristics.
It is a still further object of the present invention to provide a multiple plate friction clutch pack having plates or discs with a defined surface treatment separated by clutch friction material.
It is a still further object of the present invention to provide a multiple plate friction clutch pack wherein one surface of each clutch plate is a mill finish which is polished to define irregular flat regions and adjacent irregular recesses.
It is a still further object of the present invention to provide a multiple plate friction clutch pack for use in a motor vehicle drive line having clutch plates or discs with a surface finish of Ra 0.5 to 0.9.